Techniques for generating 3D digital data are an active area of research, for example to allow for gesture control and recording 3D scenes. There are three main range finding techniques which are interferometry, triangulation and time-of-flight imaging. The latter can be used for larger depth ranges, while triangulation is better for close ranges. to achieve a high resolution, interferometry-based methods may be used. Triangulation is a known technique wherein active lighting and an image recording device are used. Active lighting techniques make use of a specific light pattern which is projected onto a target object. Subsequently, the distortions of the detected light pattern can be used to reconstruct the depth profile.
Non-contact methods of depth profiling of surfaces, for example skin, may be required to detect and quantify surface quality, like wrinkles and fine lines. A non-contact method for close range measurement may be required where contact between the depth profiling apparatus and the surface could deform the depth profile of the surface to be scanned and lead to a false measurement. In the medical domain, depth profiling could be used to scan moles (melanocytic nevus) in the home environment and to follow the growth of the mole over time. In another field, one would possibly like to scan the surface relief structure of leaves. Depth profiling may be of interest with respect to features on the order of micrometers or greater.
Laser line scanners are known which profile 3D objects in process lines of industry whereby a laser line is imaged by an optical diffractive element and is moved across the surface of the target object. However, these require accurate motion and/or possibly tracking of either the laser line or the object to obtain 3D data of the object under investigation. Speckle noise from the laser is a limiting factor.
Another method is to use a light projector device, but these are relatively large and expensive. Moreover, projector devices are typically used for larger object like complete faces with lower depth resolution of several millimeters.
Another way of producing a particular, often complex, light pattern is by use of multiple diffractive optical elements. However, design of the diffractive element is not straightforward. Moreover further miniaturization increases the demands on the design of the diffractive optical element, with a necessity for smaller structure. There is a limit to size of the smallest structure that can be made by cost-effective means in transparent glass or plastic plate. Reference is made to US 2011/013006 A1; US 2011/040192 A1 and US 2009/118720.